Bentonite nodules

ABSTRACT

Compressed bentonite-containing nodules are disclosed as are methods for their production and methods for using them to plug wells.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates in general to filling or pluggingwells. In particular, the present invention relates to improvedmaterials for plugging wells such as drill holes within the earth andfor maintaining the plug integrity indefinitely, methods for preparingthe materials and methods for using the materials.

[0003] 2. Description of the Related Art

[0004] It has been well known to provide deep (on the order of severalhundred feet to thousands of feet) and shallow (on the order of twentyto several hundred feet) wells such as drill holes within the earth fora variety of purposes. Relatively shallow drill holes are formed duringseismic exploration, water wells, monitoring wells, cathodic protectionwells and mineral exploration and extraction wells and other purposes.Deeper holes are typically formed during standard oil, gas, and/ordisposal well operations. A deep drill hole is formed and then linedwith a casing. The drill hole generally passes through severalcompositions, such as hard compacted soil, clay, loose sand, and othertypical geologic materials, in addition to one or more water-bearinglayers. Such water-bearing layers may represent a saline water source ora fresh water aquifer. Once the well bore is determined to be unusable,the well bore is abandoned. If left unsealed, gases and/or liquidsescape from the zones of origination and migrate through the hole.Further, the casings corrode and disintegrate causing additionalmigration pathways.

[0005] In particular, a fresh water aquifer may “leak” through thecasing and hole into a fracture or uncharged zone, causing loss of waterfrom the aquifer. A drill hole extending between a saline water sourceor petroleum and a fresh water aquifer may allow commingling of thesezones, damaging both. Additionally, contamination from the surface maycause damage, such as contaminated water passing downward through thehole and casing into a fresh water aquifer. These problems can alsooccur with shallow holes.

[0006] To overcome these problems it has been known to plug the casingsand drill holes with cement. However, cement has proven less thaneffective in maintaining the integrity of the seal throughout the casingover long periods of time. One problem with cement plugs is that voidscan occur during placement of the cement slurry in the casing as aresult of incomplete displacement of drilling fluids by the slurry. Inaddition, cured cement is brittle and can crack over the life of theplug due to pressure changes or due to earthquake activity. Cured cementundergoes strength retrogression at temperatures above 230° F. if thecement does not contain additional silica. All of these factors cancontribute to limited success with cement plugs.

[0007] In the past, sodium bentonite has been proposed for filling drillholes. Early work focused on the use of finely ground bentonite forfilling relatively shallow holes. A report entitled “Axial ShearStrength Testing of Bentonite Water Well Annulus Seals” by Fred LeeOgden and James F. Ruff published by Colorado State University, 1989,discusses the use of bentonite as an annulus sealant. Past usage ofbentonite is explained in a report entitled “Experiments in SubsurfaceApplications of Bentonite in Montana” by John Wheaton, Steve Regele, BobBohman, Dave Clark and Jon Reiten, published by Montana Bureau of Minesand Geology, 1994. Both of the foregoing reports are incorporated hereinby reference.

[0008] When bentonite as ⅜″ in diameter or smaller chips is poured intoa hole it begins to expand when exposed to water. This method isadequate for shallow holes since the bentonite sinks to the bottom ofthe hole before a significant amount of swelling occurs. However, ifbentonite is poured into deep well holes, the hole may contain severalhundred feet of water.

[0009] In general, high-grade and low-grade bentonite chips fall throughwater at an average velocity of about 1 ft/sec. Smaller bentonitegranules of ⅜″ in diameter or less fall more slowly than largerparticles for two reasons. First, smaller particles have more surfacearea per unit weight, and therefore proportionally more drag in thewater. Also smaller bentonite granules are typically less dense thanlarger chips. A bentonite granule with a diameter of ⅜″ may have avolume of 0.5 cm³ and weigh 1.01 grams, while a bentonite chip with a ¾″diameter weighs 3.65 grams and has a volume of 1.50 cm³. In thisexample, the smaller granule has a density of 2.02 gr/cm³ and the largerchip has a density of 2.43 gr/cm³.

[0010] Once hydration begins, the density (or specific gravity) of thegranule decreases as the granule swells. Similarly, the fall velocity ofthe granule in water decreases at a rate of about 0.009 ft/sec perminute of fall. For instance, a small granule having an initial fallvelocity in water of just under 1 ft/sec, after 44 minutes of exposureto water, will fall at a rate of approximately 0.6 ft/sec. As thegranule absorbs water, its density decreases approaching the density ofwater further slowing the fall velocity. These factors prevent smallgranules from effectively being used to plug deep holes with severalhundred feet of water therein.

[0011] U.S. Pat. No. 5,611,400 of James et al. describes the use ofcoarse dry dehydrated ground chips of sodium bentonite as a wellplugging material. The chips are from ¼″ to about 2″ in size. U.S. Pat.No. 5,810,085 of James et al. describes the use of large pieces ofbentonite having a minimum diameter of at least ⅞″ and up to at leastabout 3 inches as a well hole-plugging material.

[0012] These patents describe relationships between particle size andparticle performance during well plugging. They point out that eachparticle expands at a rate proportional to the liquid content of theparticle. The rate of hydration of a given particle is related to thesurface area of the particle and the volume of the particle. However,the volume and the surface area of a particle vary with respect to theparticle diameter. The ratio of particle surface area to particle volumedecrease as the particle diameter increases. Accordingly, the rate ofhydration decreases (as does the rate of expansion) with increasedparticle diameter.

[0013] As noted above, it is desirable that the particles have adiameter of at least ⅞″. A particle with a diameter of less than ⅞″hydrates and may expand too rapidly to allow the particle to reach thebottom of a deep hole before plugging the hole. By way of example, finebentonite particles with a ⅜″ diameter may hydrate and swell to 10 timestheir original size and turn to a slurry state in less than 15 minutes.Often drill holes are several hundred feet deep with over a hundred-feetof liquid. Each particle falls at a rate dependent upon the particle'sdensity and the liquid's viscosity. However, generally the density ofthe bentonite and the viscosity of the liquids within the holes are suchthat a particle having ⅜″ diameter falls at a rate of one foot persecond. As the particle swells, its density decreases and its surfacearea increases, further reducing its fall velocity. Such particlesrequire several minutes to reach the hole's bottom. Accordingly, ⅜″particles may swell and plug the hole before reaching the bottom or turnto a slurry state.

[0014] Another factor which plays a part in the use of bentonite as amaterial for plugging wells, drill holes and the like is salinity.Saline water is found in many wells. High salt contents in saline watercan interfere with bentonite particles by promoting breakdown andflaking which could reduce the density of the plug when hydrated. Apreferred form of bentonite would minimize these problems.

[0015] Large-particle bentonite materials have been formed heretofore aschunks and as extrudates. Chunks are accompanied by a large quantity offines which must be removed. Chunks are irregular and often lead tobridging. Extrudates are difficult and slow to manufacture. They oftenlack physical integrity.

[0016] There is a need for an optimal large particle form of bentonitewhich is convenient to use, inexpensive to form, strong and durablewhich requires minimal removal of deleterious fines.

[0017] Listing of Background Materials

[0018] U.S. Pat. Nos.

[0019] 2,609,880

[0020] 4,886,550

[0021] 4,936,386

[0022] 5,195,583

[0023] 5,657,822

[0024] 5,810,085

[0025] “Bentonite as a Waste Isolation Pilot Plant Shaft SealingMaterial”, Contractor report, SAND 96-1968 Unlimited Release UC-721,Jaak Daemen and Chongwei Ran, University of Nevada-Reno, December 1996.

[0026] “Bentonite Well Plugging Technique”, from Field Applicationspublication by RMOTC, February 1998.

[0027] “Cement Sheath Stress Failure”, SPE 20453, Goodwin and Crook,September 1990.

[0028] “Experiments in Subsurface Applications of Bentonite in Montana”,Wheaton et al., 1994.

[0029] “Friction Factors for Hydrated Bentonite Plugs”, SPE 38347,Towler & Ehlers, May 1997.

[0030] “Geosynthetic Clay Liners Permeated with Chemical Solutions andLeachates”, Journal of Geotechnical and Geoenvironmental Engineering,Ruhl & Daniel, April 1997.

[0031] “Hydraulic Conductivity of Compacted Bentonite-Sand Mixtures”,Canadian Geotechnical Journal, Volume 29, Number 3, Kenney et al., June1992.

[0032] “Report-Axial Shear Strength Testing of Bentonite Water WellAnnulus Seals”, State University, Ogden & Ruff, Fall 1989.

[0033] “Sustained Casing Pressure in Offshore Producing Wells”, OTC11029, Bourgoyne et al., May 1999.

[0034] “Using Coarse Ground Bentonite to Plug Abandoned Holes”, MelvynJames, in WWJ, June 1996.

[0035]Handbook on Well Plugging and Abandonment, Pennwell PublishingCompany, Dwight K. Smith, 1993.

[0036] “Hydraulic Conductivity Tests on Compacted Clay”, Journal ofGeotechnical Engineering, Boynton, S.S. & Daniel, D.E., 1985.

[0037] “Mineral Water Interactions and Their Influence on the PhysicalBehavior of Highly Compacted Bentonite”, Canadian Geotechnical Journal,R. Pusch, 1982.

[0038] “State of the Art Evaluation of Repository Sealing Materials andTechniques”, Materials Research Society, Gnirk, P. 1988.

[0039] “The Effects of Brine Contamination on the Properties of FineGrained Soils”, Geotechnical Practice for Waste Disposal '87,Proceedings of a Specialty Conference, Ho, Y. A., June 15-17, 1987.

[0040] “The hnpact of a NaCl Brine on the Behaviour of Compacted FineGrained Soil”, University of Windsor, Department of Civil Engineering,Ridley, K. J. D., Bewtra, J. K. and Mccorquodale, J. A. 1983.

[0041] “Abandoned Wells”, paper by Maurice James, January 2000.

[0042] “Comments on Petro-Plug's Proposed Procedure for SealingAbandoned Oil Wells”, prepared for Maurice James by David DeGroot (UMASSat Amherst), March 14, 1998.

[0043] “Evaluation of Dispersion Characteristics of Bentonite withApplication to Design of Containment Transport Barriers”, DeGroot etal., August 1998.

[0044] “Plugging of C-1 & C-2 Monitor Wells-I Area”, Memorandum from L.A. Sessions to G. A. Johnson, Jan. 14, 1997.

[0045] “Report of Pressure Tests, Plugging Simulations”, AccordTechnologies, Ehlers, March 1999.

[0046] Comments from Dr. Roland Pusch to Craig Gardner regarding “WellAbandonment, Compressed Bentonite Questions”, Ideon Research Center,SE-22370 Lund, Sweden, June 2000.

[0047] “Design and construction of a prehydrated sand-Bentonite Liner tocontain Brine,” M. D. Haug, Barbour and Longval, 1988.

[0048] Letter and Report to Maurice James from Jerry Thornhill(Consultant) providing results from USEPA's Robert S. Kerr EnvironmentalResearch Center's Mechanical Integrity Testing Facility near Ada,Oklahoma.

[0049] Letter of Support to Maurice James from Clark Turner (Director,NPR sites in Colorado, Utah and Wyoming), Jan. 8, 1998.

[0050] Letter to Gordon Fassett (Wyoming State Engineer) from DonLamborn (Environmental Specialist) at the Pittsburg & Midgway CoalMining Co. (a Chevron Company).

[0051] Letter to Maurice James from Jack Daemen (Professor and Chair ofDepartment of Mining Engineering at University of Nevada-Reno), Mar. 22,1998.

[0052] Letter to Maurice James from R. Odell (Consulting Geologist,Minerals Scout of Rocky Mountain Scout), Aug. 22, 1999.

[0053] Petro-Plug Project Test Results, RMOTC, Tyler. Jan. 5, 1998.

[0054] Predicting Hydraulic Conductivity of Clay Liners, David E.Daniel.

[0055] Report of Well Test, Accord Group Inc., Ehlers, Oct. 27, 1997.

[0056] “Soft Sell Project Preliminary Results from the CoalingaAbandonment Pilot”, Chevron Environmental Management Company.

[0057] Technical Note, Accord Group Inc., Ehlers, Oct. 29, 1997.

[0058] “Swelling Pressure of Highly Compacted Bentonite”, University ofLulea, Div. Of Soil Mechanics, Pusch, R., 1980.

[0059] “Preliminary Report on Longevity of Montmorillonite Clay underRepository—Related Conditions,” Lund University of Technology, Pusch,R., 1990.

[0060] “Permeability, Swelling, and Radionuclide—Retardation Propertiesof Candidate Backfill Materials,” Symposium on Scientific-Basis forNuclear Waste Management, Westsik, J. H., et.al., 1981.

[0061] “New Abandonment Technology New Materials and PlacementTechniques”, Society of Petroleum Engineers #66496, Englehardt, J.,et.al., 2001.

[0062] “Waste Isolation Pilot Plant Hazardous Waste Permit”, U.S.Environmental Protection Agency I.D. Number NM4890139088, Issued to U.S.Department of Energy, 2000.

SUMMARY OF THE INVENTION

[0063] An object of this invention is to provide bentonite-basedmaterials which have properties which make them particularly suitablefor plugging drill holes. Such materials should have adequate strengthand durability to be used in drill hole plugging procedures withoutunacceptable levels of degradation and breakage.

[0064] Another object of this invention is to provide methods forpreparing bentonite materials into forms which are useful for pluggingwells and drill holes.

[0065] Yet another object is to provide such methods for manufacturingformed bentonite materials which are efficient and easily employed on acommercial scale.

[0066] An additional object of this invention is to provide methods forplugging wells and drill holes using these formed bentonite materialswhich methods are reliable when applied to a wide variety of hole depthsand configurations and which are effective in a variety of environments.

[0067] These and other objects are achieved by a new form of bentonitedrill hole plugging material. This material is in the form of compactednodules and contains bentonite and water as essential ingredients andoptionally contains other nonbentonite solids. The bentonite and waterare in admixture with the proportion of water to permit the formation ofcompacted nodules having a mean particle survival at a crush force of atleast 800 newtons and an at least 50% survival when dropped 1.5 metersonto a concrete surface. These compacted nodules of bentonite have aspecific gravity greater than 2.0. These nodules have rounded contoursand typically may be described as pillows, as spheres or as flattenedspheres. In one aspect this invention relates to this compacted nodulematerial.

[0068] In another aspect, this invention relates to methods for formingthese nodule materials. These are continuous methods and involve

[0069] a. obtaining a feedstock comprising bentonite in admixture with aproportion of water to permit the formation of compacted nodules havinga specific gravity greater than 2.0, a mean particle survival at a crushforce of at least 800 newtons and at least 50% survival when dropped 1.5meters onto a concrete surface,

[0070] b. feeding the feedstock under pressure to a continuous rollpress machine under conditions to permit the formation of said compactednodules and

[0071] c. recovering the compacted nodules.

[0072] In an additional aspect, this invention provides methods forplugging drill holes. These methods involve introducing a plurality ofnodules into the drill hole, the nodules containing bentonite inadmixture with a proportion of water to permit the formation ofcompacted nodules having a mean particle survival at a crush force of atleast 800 newtons and at least 50% survival when dropped 1.5 meters ontoa concrete surface, and thereafter permitting the feed nodules to comein contact with water in an amount and for a time adequate to cause thenodules to swell and form a substantially hydraulically solid plug inthe drill hole. In some of these methods the drill hole is empty and thenodules fall easily and directly to the bottom of the hole. In othermethods the drill hole may contain liquids. In the case where the liquidis viscous, it may be advantageous to warm the liquid, or displace theliquid such as by adding hot water, in order to assure that the nodulesfall through the viscous liquid to the bottom of the drill hole.

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] This invention will be described in more detail with reference tothe drawings. In these drawings

[0074]FIG. 1A is a side view of a representative compacted bentonitenodule of the invention. FIG. 1B is a top view of the same nodule.

[0075]FIG. 2A is a side view of a second representative compactedbentonite nodule of the invention. FIG. 2B is a top view of the samenodule.

[0076]FIG. 3A is a side view of another representative compactedbentonite nodule of the invention. FIG. 3B is a top view of the samenodule.

[0077]FIG. 4 is a cross-sectional view of a roll pressing apparatususeful in forming the nodules of this invention and useful in practicingthe methods of making of this invention.

[0078]FIG. 5A, 5B and 5C are three not-to-scale cross-sectional views ofdrill holes plugged with the nodules of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0079] In accord with this invention, bentonite feedstock is formed intonodules which are useful for plugging drill holes. In this sectionpreferred embodiments of this invention will be described. This sectionis broken into several subsections as follows:

[0080] The Bentonite Feedstock

[0081] The Nodules

[0082] Process for Preparing

[0083] Process for Plugging Wells

[0084] The Bentonite Feedstock

[0085] Bentonite is a naturally-occurring clay containing the claymineral smectite. It typically also contains accessory minerals such asquartz, mica, feldspar and calcite. Sodium bentonite is a common form ofthe mineral and is the form used herein. Sodium bentonite is primarilymined in Wyoming. Calcium bentonite is also available and often isintermixed with sodium bentonite in naturally-occurring deposits.Bentonite in which sodium bentonite predominates is preferred.

[0086] Naturally-occurring bentonite contains approximately 6-7% byweight connate water. This water is bound into the bentonite and is noteasily removable by natural drying. Bentonite includes variable amountsof nonconnate water which is in addition to the connate water. Thisnonconnate water ranges from 0% by weight of such water up to as much as15 or 20% by weight based on the total weigh of water plus bentonite.The amount will depend on the conditions of the mineral deposit, how thematerial is dried after mining, and the humidity and temperature of theenvironment in which the mineral is stored and used and the like.

[0087] In the practice of this invention, the water content of thebentonite is controlled. In describing this controlling, the connatewater is not included in water values. Thus, “bentonite” or bentonitehaving “0%” water”, has no additional water added by the manufacturingprocess but does have the 6-7% of connate water. Bentonite with “7%”water by weight has the 6-7% connate water plus 7% added water for atotal of 13-14% water by weight. When the word “bentonite” is usedherein without any qualifiers as to water content, it is intended tomean bentonite containing the 6-7% by weight of connate water.

[0088] Bentonite is available commercially as a dry material (watercontent 0%). It has a bulk density when loose of about 1.1 g/cm³. Whencompacted, its density is higher. Bentonite is also available as anundried or partially dried material having measurable water levels (forexample 2-8%). In the present invention bentonite is fed under pressureinto a roll pressing apparatus. Accordingly, the bentonite should besubstantially devoid of large intractable solids such as rocks or thelike. Preferably the bentonite used in this invention passes through an8 mesh screen.

[0089] The bentonite can be used in a substantially pure, as mined,state. It can also be used in admixture with minerals not typicallypresent in natural bentonite such as barite (another clay mineral) orthe like. Barite has a higher specific gravity than bentonite and can beadded to increase the specific gravity of the resulting nodules. Thiscan assist in speeding the descent of the bentonite nodules to thebottom of a drill hole, particularly in cases where the drill holecontains water or other liquids. These materials are referred to as“nonbentonite” minerals or solids.

[0090] Nonmineral materials can be added to the bentonite feedstock toalter the characteristics of either the nodules themselves or the plugthat forms when the nodules contact water and swell. These materials arereferred to as “additional materials” and have been described in theliterature of well drilling and well sealing heretofore and include, forexample, wood chips, walnut shells, cellophane strips, nylon chop, wooland the like.

[0091] Nonbentonite solids are completely optional components of thefeedstocks. Typically they are less than half the total solids. Thus theproportion of nonbentonite solids/bentonite can range from 0/1 to 1/1and more commonly can range from 0/1 to 0.5/1 by weight.

[0092] The feedstock always contains the connate water and may containadditional water above the connate water. The amount of additional wateris controlled to provide the desired durable nodules and to permit theirproduction in standard roll press equipment. The amount of additionalwater, as a weight percentage, based on the weight of added water plusbentonite is from about 2% to about 20%, preferably from about 5% toabout 20%, more preferably from about 10% to about 20% and especially 12to 16%.

[0093] Thus, overall feedstock compositions are as follows: Bentonite 35 to 98% by weight Nonbentonite minerals   0 to 45% by weight Water(nonconnate) 2.0 to 20% by weight Preferably, Bentonite  45 to 95% byweight Nonbentonite minerals   0 to 35% by weight Water (nonconnate)   5to 20% by weight more preferably, Bentonite  50 to 90% by weightNonbentonite minerals   0 to 30% by weight Water (nonconnate)  10 to 20%by weight. and especially, Bentonite  64 to 88% by weight Nonbentoniteminerals   0 to 20% by weight Water (nonconnate)  12 to 16% by weight.

[0094] As noted above, the feedstock can contain additional materials,if desired.

[0095] The Nodules

[0096] The bentonite-containjg feedstock is formed into nodules for useas a well hole-plugging material. As used herein, a “nodule” is definedto be a solid continuous body having substantially its entire exteriorsurface compacted smoothly into a rounded shape. As shown in FIGS. 1through 3, the nodules can have a variety of shapes. To achieveefficient use in drill hole plugging operations, it is desirable that.the nodules have generally rounded surfaces. This assists in achievingdense packing in the drill hole and tends to minimize bridging in thedrill hole. One common shape, a “pillow” shape, is shown in FIGS. 1A and1B. As can be seen, this shape presents rounded comers and is somewhatsquared off in top view. In this nodule the largest cross-sectionaldimension is denominated DM and the smallest dimension is denominatedDm. During production of nodules in a roll press, DM is the dimensionacross the face of a roll press cavity and Dm is the combined “depth” or“thickness” of the two cavity halves.

[0097] Another possible nodule shape is substantially spherical. Ourresults suggest that a true sphere would give excellent down-holesealing performance. Such a shape is shown in FIGS. 2A and 2B. Again DMis the largest dimension. It is often difficult to get good, completefilling of true spherical nodule-forming cavities in a roll press.Accordingly, for this practical reason, it is preferred to use noduleshaving a somewhat flattened spherical cross-section. Such an “oval” or“elliptical” cross-section nodule material is shown in FIGS. 3A and 3B.As can be seen from these drawings, the ratio of DM:Dm can range fromabout 1:1 (as shown in FIG. 2) to about 2:1 or 3:1 as shown in FIGS. 1and 3. We have had best results in terms of nodule compaction, rollpress cavity fill and consistent release from the roll press cavitieswhen the ratio DM:Dm is from about 1.01:1 to about 3:1, preferably about1.05:1 to about 2.5:1 and especially from about 1.5:1 to about 2.25:1.

[0098] The size of the nodules is controlled. When the nodules are to beused as a well plugging material the preferred minimum size for DM isabout ⅞″. The maximum size for DM depends in part upon the diameter ofthe drill holes and wells in which the nodules are to be used.Typically, DM should not exceed about 0.67 times the diameter of thedrill hole and preferably should not exceed 0.6 times the drill holediameter. Many common drill holes are from about 5″ to about 8″ indiameter but some wells can reach 18″ or 24″ or greater in diameter. Ourwork has focused on plugging 5″ to 8″ diameter wells and with thelargest nodules we have made, DM has ranged up to about 3 to 4 inches.For this size drill hole, and considering the sizes of cavities whichcan be easily employed in a roll press, the preferred sizes for DM rangefrom about 1″ to about 5″, more preferably from about 1.5″ to about 4″and especially from about 2″ to about 3.5″.

[0099] While these materials have worked well, one could envisage largernodules (DM equals up to 6″) for use in larger diameter wells.

[0100] Many of the advantages of the high strength compacted nodules ofthis invention are also realized with smaller sizes such as noduleshaving ¼″ to about ⅞″ DM values. These smaller nodules can be used forwell plugging as herein described and can also find application in morespecialized sealing operations such as sealing or plugging betweencoaxial casings or anular sealing around joints in a casing string. Inthese applications, their smaller size can be advantageous.

[0101] The nodules of this invention should be durable. If they arefragile an unacceptable proportion of fines and shards will form duringnormal handling and drill-hole-filling procedures. It has been foundthat if, on average, the nodules have a mean particle survival at acrush force of at least 800 newtons and can survive at least 50% of alldrops of 1.5 meters onto a concrete surface, they will give acceptableperformance as a drill hole plugging material. More preferred nodulescan withstand 100%, of all 2 meter drops and have a mean particlesurvival at a crush force of at least about 900 newtons.

[0102] The nodules have a controlled high density as a result of thecompacting. Their density ranges from about 2.00 g/cm³ to about 2.5g/cm³ and preferably 2.05 g/cm³ to 2.25 g/cm³. If substantial amounts of“additional materials” were added this could lower the density below 2.0g/cm³. This would generally not be desirable.

[0103] Process for Preparing

[0104] The nodules are formed by compressing the feedstock into aforming mold. This can be carried out in a roll press. As shown in FIG.4, a roll press includes a pair of rolls 1A and 1B which are driven inopposite directions. The clearance between the rolls can be adjustedsuch as by hydraulic system 4. This can adjust the degree of compactionapplied to the feedstock when it is formed into the nodules.

[0105] Each of the rolls carries a plurality of cavity halves, such ascavity halves 2 a, b, c and d on roll 1 a and cavity halves 2 e, f, gand h on roll 1B. These cavities are positioned so that as the rollsturn, cavity halves pair up to create a cavity corresponding in shape tothe shape of the final nodule. In FIG. 4, cavity halves 2 d and 2 h aredepicted forming such a cavity.

[0106] Feedstock is placed in feed hopper 10 and fed to the rotatingrolls by screw feeder 5. The feedstock fed via screw drive feeder 5passes though feed adapter 7 which is designed and sized to direct theproper amount of feed to the cavities as they are being formed. Theclearance between the feed, adapter and the rolls and the relativevelocity of the screw drive can be varied to adjust the pressure appliedto the feedstock during compaction into nodules. 6 is a bearing blockfor the drive. 9 is a paddle mixer in the feed hopper which assuresproper filling of the drive screw. The nodules, such as shown as 3, whenformed, are ejected from the rollers and are collected in product chute8.

[0107] The feedstock is compacted under pressure. This is a pressure ofat least about 1 MPa, preferably at least about 3 MPa and especially atleast about 5 MPa, such as from about 5 MPa to about 20 MPa. The rollpress is operated at a speed of from about 2 RPM to about 50 RPM,preferably 3 RPM to about 40 RPM and especially 5 to about 25 RPM beingmost common.

[0108] The roll press will generate substantial heat due to frictionresulting during the compaction process. This is usually acceptable andmay cause the outer surfaces of the nodules to dry and anneal slightly.If heating becomes excessive, heat can be removed by means not shown.

[0109] Process for Plugging Wells

[0110] The nodules of this invention are used for plugging wells. A“well” is defined by the United States Environmental Protection Agencyto be a hole in the ground that is deeper than it is wide (40 CFR). Thatdefinition is used herein, as well.

[0111] Representative wells plugged in accord wiih the invention includedrill. holes made in connection with oil and gas exploration andextraction including production wells, injectors, seismic holes, and thelike. Other representative wells include drill holes and shafts producedin connection with mineral extraction, water production and wastedisposal, to name but a representative sample.

[0112] In this use, nodules are introduced into the drill hole or otherwell by pouring or pumping and allowing the nodules to free fall to thebottom of the drill hole. They can be introduced using water-permeablesleeves, copper carriers, and the like. The nodules can be suspended ina fluid such as water or a mud, such as a bentonite-containlngabandonment mud and injected to the desired location using pumps or thelike.

[0113] In one application, the bentonite nodules can be placed over theentire length of a well, substantially filling it and providing abentonite plug over the entire length of the drill hole.

[0114] As illustrated in FIG. 5A, in another application, the bentonitenodules can be placed at the top and bottom of a drill hole or otherwell. A nonbentonite material can be used between the two layers ofnodules to support the top layer until it swells.

[0115] As illustrated in FIG. 5B and 5C, in other applications thebentonite nodules can be placed at the top and bottom of a drill holeand at other locations in the drill hole to achieve plugs betweenvarious formations or layers.

[0116] When using the compressed bentonite nodules of this invention toplug drill holes it sometimes happens that a layer of higher viscosityliquid is present in the drill hole or other well. This is most commonlya layer of crude oil floating upon a layer of water in the drill hole.In this case, the viscous oil layer may provide resistance to thenodules or other solids, such as gravel, and prevent them from easilyfalling to the bottom of the drill hole. The bentonite nodules detainedby the oil layer can pick up water, swell and bridge the drill hole atan inappropriate depth. Adding heat to the drill hole prior to addingthe bentonite nodules can be helpful in solving this problem as the heatreduces the viscosity of the oil layer and decreases the likelihood thatthe nodules will be held up for a long period in the oil layer.

[0117] Heat may be added in any manner. This could include passing aflow of steam or hot gas into the oil layer. However, most drill holeplugging operations take place in settings where drill holes are beingabandoned. Thus the drill hole typically does not have pipes or othermeans for delivering steam or hot gas to the oil layer. In addition,there is often no equipment on site for producing steam or hot gas. Inthese settings, however, it is often possible to obtain hot water. Hotwater can simply be poured into the drill hole to warm the oil layer.

[0118] In a drill hole setting, hot water is most commonly from about115 to about 180° F. and more typically from 125 to 175° F. andespecially 130 to 150° F. One can add from about 1 to 10 barrels of hotwater to a drill hole while larger amounts of up to about 100 barrelscan-also be used if desired.

[0119] The amount of heating is often varied to suit the particularcircumstances of a particular drill hole. A large excess of heating istypically not the answer as it takes extra time and involves unneededexpense. In addition, it also can lead to conditions where anunnecessarily elevated temperature causes the bentonite to expand toorapidly when a bentonite nodule is traversing the oil layer which can inturn lead to undesired bridging of the drill hole.

[0120] Another factor to consider when using nodules of bentonite toplug a well is the salinity of any water in the well. In many casessality will not be a limitation but if the water is highly saline, insome cases the nodules may exfoliate and break up. The hydration stilltakes place but the nodules have been granulated and the plug producedwill likely have less density and therefore higher permeability thandesired for the purpose of well plugging. This problem can be solved fordifferent salinities by varying the water saturation in the nodulesthemselves, by slightly pre-hydrating the nodules prior to wellplacement or alternatively by diluting the salinity of the water in thewell bore during placement of the nodules. Compacted nodules of thisinvention were tested at three levels of salinity—fresh water, sea water(19,000-23,000 mg/L chlorides) and saturated brine (189,000 mg/Lchlorides). The compacted nodules exhibited markedly differentcharacteristics than are typically observed with noncompacted materials.Compacted nodules containing about 16% by weight nonconnate water gavegood results and exhibited only minor exfoliation and break down.

[0121] In all cases, the bentonite nodules swell when contacted withadditional water and form a hydraulically solid plug of expandedbentonite containing about 38% by weight water.

EXAMPLES

[0122] The invention will be flrter illustrated by the followingexamples. These are provided to demonstrate the practice of thisinvention and are not to be construed as limitations on the inventionwhich is defined by the claims. The examples were conducted and recordedin a format used previously for briquet making. The report descriptiontherefore at times labels the nodules as “briquets”. Some of the datawere recorded in international system of units while other data wererecorded in English units. Conversions between these units can becarried out using factors taken from the following conversion table.CONVERSION TABLE INTERNATIONAL SYSTEM OF UNITS (SI) TO ENGLISH UNITS 1[mm] 0.03937 [in] 1 [g/cm^(3]) 62.42000 [lb/ft^(3]) 1 [t] 2,204.60000[lb] 1 [t/h] 2,204.60000 [lb/h] 1 [N] 0.22480 [lb] 1 [MN] 224,809.00000[lb] 1 [MN/m] 5,710.16000 [lb/in] 1 [MPa] 145.03800 [PSI] 1 [kW] 1.34100[HP]

Example 1

[0123] K. R. Komarek model B100R, B220QC and B400A roller presses wereused in all trials. FIG. 4 shows schematically the cross section ofthese machines. Feedstock material from the feed hopper was suppliedinto the roll nip with a horizontal screw, driven by a variable speeddrive unit. A paddle mixer was utilzed to agitate feedstock materialinto the horizontal screw at the feed inlet.

[0124] The material was then compacted between two rolls which arecantilevered on the ends of shafts outside the bearing blocks. A fullyadjustable hydraulic system provides the force holding the rollstogether. This force is equal in magnitude to the roll-separating forcegenerated by the compacted material in the roll nip. A gas-filledaccumulator in the hydraulic system acts as a pressured reservoir.Accumulator pre-charge pressure determines the hydraulic systemstiffness.

[0125] Feedstocks described in Table 1, made up of bentonite withvarious water contents, were placed into the feed hopper. Theroll-pressing process was then tested. After the roll press wasoperating under stable conditions, all the data were collected. Thesedata presented in Table 2. The properties of the nodules produced in thetests are listed in Table 3.

[0126] Two methods were used to compare nodule strength:

[0127] A. Crushing Strength.

[0128] The nodule was placed between two parallel plates and loadeduntil failure. Nodule strength is expressed as the maximum force thenodule resists before failing.

[0129] B. Drop Strength.

[0130] The nodule was dropped on the concrete floor. Drop strength wasdefined as the height of drop at which more than 50% of nodules start tobreak because of impact. If the drop strength was over 2.0 m, the numberof drops from 2.0 m was additionally recorded.

[0131] The nodules were flattened spheres shaped as shown in FIG. 3 withDM=2.97″ and Dm=1.5″.

[0132] As can be seen from the product data given in Table 3, thenodules are compacted and durable.

Example 2

[0133] A series of nodule preparation runs were conducted on a Komarek B400B roll press machine. The nodule size was 2¾ inches by 1¾ inches.

[0134] The roll clearance was 0.060″. A variety of bentonite feedstocksvarying in water content was employed.

[0135] One first set of 9 runs was made with dry bentonite (essentiallyno added water).

[0136] The initial run was made with the hydraulic pressure set at 1100psi and the rolls and feed screw run at 58 RPM and 25 RPM, respectively.The indicated pressure shot up beyond 2000 psi. The action appeared tobe stiff.

[0137] Another initial run was made with the feed screw slowed down to15 RPM. This was done in case the 1100 psi machine setting wassufficient. In both initial runs, nodules were formned, although theywere unacceptable as they were being crushed and split duringproduction.

[0138] Because of these results, the hydraulic pressure was decreased to700 psi, the roll was kept at a full 60 RPM and the feed screw sloweddown to 10 RPM. Nodules were produced at first, but they were not wellformed and still appeared to be crushed and brittle.

[0139] Run 2 was performed with the roll drive at a full capacity of 60RPM. The feed screw was run at 13 RPM but the nodule quality did notsignificantly improve.

[0140] Feed screw speed was slowed to 11 RPM and the roll speed slowedto 58 RPM as well. Hydraulic pressure was set to 600 psi. Nodule qualitywas slightly better.

[0141] In the next run, the pressure was increased to 700 psi with allother conditions being the same. The needle on the gauge showed a morecontrolled response, and the nodule quality was the best thus far,although not particularly strong.

[0142] In order to determine the range of pressure under differentconditions, the next run was done at 850 psi with the same roll speedand a slightly faster feed screw (13 RPM). The machine became verysensitive. Thus, the next run was made with the same conditions but withthe pressure dropped to 600 psi. The nodule quality was improved.

[0143] Another run was made to determine the bottom range of the feedscrew at a lower pressure. At 500 psi, with the feed screw at 11 RPM andthe rolls at 58 RPM, quality nodules were made. They were slightly roughabout the edges, but otherwise they were aligned.

[0144] Run 8 was done in the same way with the rolls run at maximum. Thenodules were as good as in the previous run.

[0145] Given the above data, it appears that the optimal pressure rangefor the machine is between 500 and 600 psi. 700 psi is possible. Therolls can be run as high as 58-60 RPM under these conditions, but thefeed screw must be run at a slow 11 RPM with a maximum of 13 RPM beforethe machine becomes very sensitive.

[0146] Just to re-verify the pressure, a small run was done from withthe optimal feed and roll speeds but at 400 psi pressure. The noduleswere still of good quality, but not as good as the runs that determinedthe optimal conditions.

[0147] Hence, when the conditions are optimal, the nodules are verystrong, of excellent quality, and the needle on the hydraulic pressureshows very slight deviations from its set pressure indicating a goodspring effect.

[0148] Further runs were performed in order to fully exploit the rangeof quality nodules. The previous nodule, particularly of run 5 at 0%moisture, was a good nodule, so it was to be determined if a higherquality nodule was possible.

[0149] In the next series of runs, the feedstock was changed. Abentonite material of 7% moisture was used. The bentonite with thisadded moisture showed improved roll pressing. It was also found that thematerial was easily briquetted in general, requiring less hydraulicpressure than with dry material. In order to verify this, the pressurewas kept at 300-400 psi for each run. The response in the pressurereadings was much more favorable than had previously been observed. Inaddition, the nodules were showing improved quality, with excellentstrength. Alnost all nodules survived 2 meter drop tests, and a goodnumber survived drops of as much as 5 meters.

[0150] Though these nodules were quite good, there still seemed to be alot of sensitivity in the hydraulic pressure responses in the rollpressing, and when the 7% moisture material was depleted, 14% moisturefeedstock material was used to focus on the pressure response and motorspeeds.

[0151] With 14% moisture content, it was seen that the nodules showedimmediate improvements in roll pressing from just the moisture alone.The moisture content of 14% seemed to be quite ideal. For the first fewruns, the pressure was lowered to 300 psi in an attempt to improve thesurface quality by eliminating cracks and clam shelling from too highpressures, and the motors were run to compensate and improve strength.The third 14% moisture run showed a well-developed nodule.

[0152] A continuous, steady production run was also sought. The next fewruns were made not only to meet these objectives, but to get a betterdetermination as to the range of speeds available. A lower pressure wasfound to work quite well, and this is beneficial as it extends the rolllife of the machine. Fuller nodules were made with the correct feed ofmaterial from the feed screw. The rolls had the most range of operationavailable to them, being able to run in a bit slower, or even at fullcapacity.

[0153] With each run, the nodules would improve but the belts were aptto slip. After correcting with the pressure and the feed screw speed,the optimal running conditions were narrowed down and locked into aspecific range. The nodules had improved so much that they were of theutmost in strength, quality and appearance for this size. This goodproduct quality was present during a continual and lengthy run.

[0154] The results for all of the above trials are in Table 4. It hasbeen shown that the higher amount of moisture (14%) is very beneficialto high quality manufacturing. Best results were obtained with thefollowing conditions.

[0155] With 14% moisture:

[0156] Hydraulic pressure: 250 psi

[0157] Roll Cycles/Load: 58-60 RPM

[0158] Screw cycles/Load: 12-13 RPM

[0159] With 7% moisture:

[0160] Hydraulic pressure: 300 psi

[0161] Roll Cycles/Load: 52-54 RPM

[0162] Screw cycles/Load: 11 RPM

[0163] With 0% moisture:

[0164] Hydraulic pressure: 500-600 psi

[0165] Roll Cycles/Load: 58-60 RPM

[0166] Screw cycles/Load: 11 RPM

[0167] (If material flow is good and consistent from the feed inlet, 700psi and 13 RPM on the screw is possible.)

Example 3

[0168] The nodules formed as a result of the knowledge gained fromExamples 1 and 2 were evaluated in the laboratory and in the field.

[0169] Laboratory Tests

[0170] Test No. 1

[0171] The effect of salinity on compressed bentonite nodules' abilityto form a hydraulically solid plug was evaluated. Nodules containingabout 16% by weight nonconnate water were used.

[0172] Test Methodology: Freshwater

[0173] Nodules were placed in a mason jar, covered with freshwater, andthe jar was closed with a lid. On visual inspection, within 12 hours thenodules had hydrated to form a solid plug and consumed the water in thejar.

[0174] Test Methodology: Seawater

[0175] A sample of Gulf of Mexico seawater (19,000-23,000 mg/Lchlorides) was used. Nodules were placed in a jar, covered withseawater, and the jar was closed. Within a few minutes some of thebentonite was observed flaling off of the nodules. Twelve hours later,the nodules had formed a hydraulically solid plug and consumed the waterin the jar.

[0176] Test Methodology: Saturated Sodium Chloride

[0177] A sample of saturated sodium chloride brine (189,000 mg/Lchlorides) was used in the same test. Within a few minutes, some of thebentonite was observed flaking off of the nodules. Twelve hours later,the nodules had formed a hydraulically solid plug and consumed the waterin the jar.

[0178] This showed that in most cases there may be no sainty limit onthe ability of compressed sodium bentonite nodules to form ahydraulically solid plug. However, extremely high salinity levels maylead to some desiccation and exfoliation of the bentonite nodules. Thiscan occur as the nodules fall through a layer of extremely saline water.

[0179] Test No. 2

[0180] This test was to determine what happens to a compressed sodiumbentonite nodule-based plug that has been hydrated in freshwater andthen is placed in a saline water environment.

[0181] Test Methodology: Saltwater Bath of Freshwater Plug

[0182] A wire mesh container for the nodules was fashioned to allow forobservation of the plug from all sides. Nodules were placed in thecontainer and immersed in freshwater and allowed to hydrate overnight. Asolution of saturated salt water (189,000 ppm chlorides) was prepared.The wire mesh container was removed from the freshwater and immersed inthe saltwater bath. The salinity of the saltwater solution wasperiodically measured based on its conductivity. Although initiallythere was a slight decrease in conductivity of the saltwater, thesalinity recovered and stabilized. The plug continued to hydrate. Noshrinkage was observed, and no deterioration of the plug was observed.The test ran for over 60 days.

[0183] This test shows that desiccation does not take place in apresaturated fresh water condition.

[0184] Test No. 3

[0185] The test was to determine whether the nodules will be washed awayby water running through an unhydrated plug.

[0186] Test Methodology: Bentonite Washout

[0187] A clear plastic container with holes in the bottom was filledwith compressed bentonite nodules. Water was continuously run throughthe container. The run-off solution was inspected of bentoniteparticles. Within 3 hours, the bentonite had hydrated sufficiently toretard the flow to negligible amounts. The container became deformed dueto the swelling of the nodules as they hydrated. There was a minorclouding of the water utilized for the experiment. This indicated thatwashout would not be a problem.

[0188] Test No. 4

[0189] A test was conducted to determine whether an oil coating and anoily water environment would inhibit hydration of the compressedbentonite nodule.

[0190] Test Methodology: Hydration in Oily Environments

[0191] A jar was filled with oily produced water, 19° API, with a freeoil layer that was thicker than one nodule. Nodules were individuallydropped through the oil layer into the jar. Twelve hours later thenodules had formed a hydraulically solid plug. The only liquid remainingin the jar was free oil. All of the water was consumed by the nodules.The presence of oil or oil coating of the nodule did not affect thehydration rate since there was access to water.

[0192] Test No. 5

[0193] The effect of steam flow created prior to complete hydration of acompressed sodium bentonite plug was studied to determine if the steamwill prevent sealing of the open flow paths.

[0194] Test Methodology: Hydration in Steam Environments

[0195] A mason jar was layered with pea gravel, bentonite nodules andmore pea gravel. 200° F. freshwater was placed in the jar. The jar washeated, producing boiling water and steam escaping through apreferential flow path. Within two hours, the open flow paths wereobserved to have sealed due to hydration of the bentonite. Theexperiment was suspended. The test jar was set aside. Two days later,observation of the jar suggested that swelling pressure had broken thejar, but the gravel and the bentonite had formed a solid plug. The steamand boiling agitation had distributed bentonite particles throughout thegravel pore spaces. Preferential flow paths did not remain open duringthe experiment due to hydration.

[0196] Test No. 6

[0197] The effect of hydrogen sulfide on bentonite hydration wasexamined.

[0198] Test Methodology: Hydration in H₂S Environment

[0199] A nodule was immersed in a jar of freshwater while at the sametime another nodule was placed in a jar of saturated hydrogen sulfidewater. Both nodules hydrated. By visual inspection, the nodule in thehydrogen sulfide water swelled about 70 percent as much as the nodule infreshwater. This showed that bentonite will hydrate in saturatedhydrogen sulfide water. However, bentonite swelling capacity appears tobe affected by the presence of H₂S.

[0200] Field Tests

[0201] Three generalized drill hole plugging designs were tested. Thethree designs were dependent upon the presence of freshwater and thecalculated top of cement. The principle utilized in the design was torestore well bore flowpaths to their preexisting states. In short, whereclay once resided, place clay; where porous and permeable formationsexist, place like material, including intervals across perforations.This, in effect, would return the material from whence it came. As willbe described below, the plug was to be 110 feet in total length.

[0202]FIG. 5 depicts the three design schemnatics.

[0203] Case 1—No Freshwater Present

[0204] As shown in FIG. 5A, a plugged well 20 is made up of a cementwell casing 22 extending from the topmost perforation 24 of producingzone 26 to the surface 28. Alternatively, the well casing 22 couldextend from a water shut off or from a linear top (whatever is highest)to the surface 28.

[0205] This plugging called for the isolation of the producing zone 26from the surface through the placement of a 110 ft. zonal plug 0. Inaddition to the zonal plug, a 25 ft. surface plug 32 was placed.

[0206] To ensure that the bentonite plug 30 provided an effective sealaround the liner top, it was decided to extend the bottom of the zonalplug 30 by ten feet, penetrating the liner, if present, and, at times,reaching below the topmost perforations or water shut-off. This ten footextension is identified as 34. Using the same logic, the surface plugwas also extended an additional twenty-five feet as shown at 36 toensure isolation.

[0207] The space between plugs 30 and 32 was filled with gravel 38.

[0208] Of the nineteen wells plugged in the field test, eleven were ofthe Case 1 design.

[0209] Case 2—Freshwater Present. Cement in Annulus Above FreshwaterInterface

[0210] As shown in plugged well 40 in FIG. 5B, when freshwater ispresent, such as at level 42, an operator is required to protect it frompotential contamination from both the producing zone 26 and the surface28. Although the annulus at and near the freshwater interface 42 isprotected from corrosive formation waters by a sheath of cement 22, in aCase 2 well, should the integrity of this sheath fail, the potential forfreshwater contamination is great. Therefore, in addition to theproducing zone plug 30 and the surface plug 32, an operator is alsorequired to place a 100 ft. plug 44 across the freshwater interface 42.By design, this plug should effectively shut off the possibility forcommunication from both above and below. Gravel fills regions 38 and 46.

[0211] There were four pilot wells of the Case 2 design which wereplugged.

[0212] Case 3—Freshwater Present. Cement Top in Annulus Below FreshwaterInterface

[0213] As shown in FIG. 5C, the bentonite nodules can also be used toplug wells such as well 60 where the concrete annulus 22 does not extendall the way to the surface 28 and in which freshwater 42 may be found inthe region between the top of the concrete annulus and the surface. Inthis case, producing plug 38 and surface plug 32 are substantially asshown in FIGS. 5A and 5B.

[0214] It was proposed to fire a cavity shot at the base of freshwater42, and subsequently fill the hole and cavity 46 created by the cavityshot with bentonite nodules. Cavity shots are currently the requiredmethod when more than one string of casing is present at the base offreshwater.

[0215] The abandonment would be completed in two phases, the initialproducing zone plug 30, then the cavity shot (with a rat-hole providingfor the encasing of debris within bentonite) and the freshwater plug 46and the surface plug 32.

[0216] There were four wells plugged utilizing the cavity shot technique(Case 3).

[0217] Field Results

[0218] Plugging of nineteen wells within a Coalinga, California oilfield was completed utilizing compressed, preformed bentonite nodules,which serve as a permanent clay barrier to fluid migration within thewell bore. The following section details the execution at the fieldlevel, and the results obtained. The results are summarized in Table 5,as well.

[0219] Implementation

[0220] Bentonite nodules were to be used in lieu of cement, with gravelused as fill material. One of the benefits of the bentonite process overconventional cement abandonments is the lack of need for customarycement pump trucks, coiled tubing units and bulk cement units. In orderto accomplish the objectives, the pilot wells were divided into twodiscrete subsets: the first ten wells where placement success wasconsidered the highest objective; and the second nine wells where thefocus was directed towards process efficiency. The results of thepluggings are summarized below and in the Table 5.

[0221] Pilot Learnings

[0222] Nineteen wells in the Coalinga Oil Field were plugged usingcompressed bentonite nodules. Eleven of the wells were of the Case 1design, while the remaining eight were equally split between Case 2 andCase 3.

[0223] The densely compacted bentonite nodules fell through the firstten wells attempted (predominantly primary producers) without incident.The bentonite was placed into the wells utilizing a chute and finnel ata rate of about one forty pound box per minute. The bottom plug 30 wastypically placed by pouring the bentonite dry, without the presence ofwater, from surface and allowing it to hit the air/liquid interface,which was approximately 1,000 feet below ground level. The nodulesconsistently penetrated the interface without bridging and fell throughthe liquid column to the desired depth.

[0224] Upon witnessing the placement of the plug 30, water was thenadded, if needed, to hydrate the plug. It should be noted that properplug hydration was ensured and verified through the sampling offormation liquids prior to material placement to ascertain adequatewater cuts, and the sustained presence of standing water upon executionof subsequent stages within a given well's abandonment.

[0225] Pea gravel and larger sized gravel (¾″-minus) 38 was used in thepilot. The larger sized gravel was preferred as it more closelyapproximated the size and density of the bentonite nodules.

[0226] The temperature and timing of water placed in the well alsovaried during the plugging of the first ten wells. This had a pronouncedeffect on bridging, as is discussed below.

[0227] Subset No. 1: First Ten Wells

[0228] Two means of placing bentonite and gravel were explored duringthe plugging of the first ten wells: dry pouring, and pouring into acolumn of liquid. Initially, material was poured into the well and wateradded after the proper bentonite depth was verified. Since the peagravel and the ¾″-minus gravel both were observed to bridge occasionallywhile free-falling several hundred feet to the air/liquid interface, itwas decided to fill the entire well bore with water to minimize theseevents. This did result in the elimation of gravel bridging, but alsodecreased the application rate at the surface, and increased thesettling time downhole considerably. There was, however, a netimprovement when considering the downtime caused by bridging.

[0229] In addition, the temperature of the hydrating water was alsovaried in an attempt to reduce the viscosity of the heavy oil,especially at the fluid interface. The combined effect of wellbornfill-up, with hot water (approximately 130° F.), a process derived bythe end of the first ten wells, appeared to have solved the placementand bridging issues.

[0230] The addition of hot produced water preceding the introduction ofabandonment materials and between the alternating stages of bentoniteand gravel also improved efficiency by reducing the number of gravelbridge-offs.

[0231] Subset No. 2: Last Nine Wells

[0232] The focus of the last nine wells was to improve the placementrate of gravel and bentonite nodules. The first ten wells identified aneed for water during gravel placement, coupled with the realizationthat hot water would reduce the fluid viscosity at the interface.Therefore, it was decided to fill the wells partially with hot-waterupon the commencement of abandonment work. Prior to adding gravel andbentonite, the wells were treated with a minimum of one casing volume ofhot water.

[0233] This modification resulted in the elimination of gravel bridging.Unfortunately, after placing the first bentonite plug, the slicklineunit indicated that the bentonite had bridged high. This was the firstoccasion in which the bentonite had not fallen to its intended depthwithout incident. Unsure of the cause, and suspecting somecharacteristic particular to this well alone (perhaps the higher gravitycrude oil present), the operations crew proceeded to bridge twoadditional wells with bentonite utilizing the same new technique, hotwater with bentonite.

[0234] It was at this time that the effects of heat on bentonitehydration were fully understood at the field level. Prior use of hotwater in the first ten wells was used after placing bentonite and beforepouring gravel. Now, hot water was constantly being added to the wellwith no opportunity for downhole cooling to occur prior to the additionof bentonite.

[0235] The predicament for operations was the need for hot water toassist in viscosity reduction for the gravel's sake, and the need forcool water to ensure effective placement of bentonite. The solutionobtained was to allow the bentonite to free-fall as much as possible inthe well bore to reduce settling time and achieve a high confidencelevel of it reaching its objective depth. Once there, and verified witha slickline tag, hot water could be trickled into the well while gravelwas poured. The water then served to hydrate the bentonite and preventgravel bridges.

[0236] As a further means of optimization, the trickling of the hotwater into the well was stopped prior to the end of the gravel stage.This served to cool the water before the introduction of bentonite.

[0237] The modified placement technique made for an efficient andeffective plug. In every case, the bottom plug hydrated fully, asevidenced by standing columns of fluid at the surface before theplugging was even completed. As a result, subsurface plugging time wasreduced.

[0238] Additionally, a core was taken of the surface plug of a well forthe purpose of obtaining its permeability. The core was taken at a depthof approximately eleven feet from the surface after the conductor andsurface casing were cut-off. Upon removing the casing, a hydraulicallysolid plug was exposed from which the core sample was obtained. Testsindicated that the plug had an air permeability of less than 0.1 (lessthan the lowest measurement the apparatus can obtain), a waterpermeability of 0.0014 and a hydraulic conductivity of 1.44×10-9 cm/s.TABLE NO. 1 FEED MATERIAL PROPERTIES DATA SHEET - BATCH 1. CHEMICAL NAMEBENTONITE MOLECULAR FORMULA SAMPLE MARKED “BH#4” MOISTURE CONTENT % 18.5TRUE DENSITY g/cm³ BULK DENSITY (LOOSE) g/cm³  1.11 BULK DENSITY(PACKED) g/cm³  1.24 HARDINESS MOHS SCALE ANGLE OF REPOSE deg NOTMEASURED ANGLE OF FALL deg ANGLE OF DIFFERENCE deg OTHER MATERIALRETAINED ON SIEVE MASS MASS MESH MICRONS MASS g FRACTION % ACCUMUL %  82380 7.4 2.7 2.7  18 1000 63.2 23.5 26.2  35 500 68.1 25.3 51.5  70 21062.4 23.2 74.7 140 105 39.2 14.6 89.2 200 74 14.1 5.2 94.5 325 44 0.70.3 94.7 PAN #N/A 14.2 5.3 100.0 FEED MATERIAL PROPERTIES DATA SHEET -BATCH 2. CHEMICAL NAME BENTONITE MOLECULAR FORMULA SAMPLE MARKED “12-40”MOISTURE CONTENT % 10.2 TRUE DENSITY g/cm³ BULK DENSITY (LOOSE) g/cm³ 1.09 BULK DENSITY (PACKED) g/cm³  1.18 HARDINESS MOHS SCALE ANGLE OFREPOSE deg NOT MEASURED ANGLE OF FALL deg ANGLE OF DIFFERENCE deg OTHERMATERIAL RETAINED ON SIEVE MASS MASS MESH MICRONS MASS g FRACTION %ACCUMUL %  8 2380 5.2 1.7 1.7  18 1000 110.8 36.0 37.7  35 500 135.443.9 81.6  70 210 55.8 18.1 99.7 140 105 0.4 0.1 99.8 200 74 0.2 0.199.9 325 44 0 0.0 99.9 PAN #N/A 0.3 0.1 100.0 FEED MATERIAL PROPERTIESDATA SHEET - BATCH 3. CHEMICAL NAME BENTONITE MOLECULAR FORMULA SAMPLEMARKED “GRAN. FINES” MOISTURE CONTENT % 9.1 TRUE DENSITY g/cm³ BULKDENSITY (LOOSE) g/cm³ 1.16 BULK DENSITY (PACKED) g/cm³ 1.28 HARDINESSMOHS SCALE ANGLE OF REPOSE deg NOT MEASURED ANGLE OF FALL deg ANGLE OFDIFFERENCE deg OTHER MATERIAL RETAINED ON SIEVE MASS MASS MESH MICRONSMASS g FRACTION % ACCUMUL %  8 2380 0.4 0.1 0.1  18 1000 1.5 0.5 0.6  35500 3.8 1.2 1.7  70 210 151.0 45.8 47.6 140 105 84.5 25.6 73.2 200 7426.3 8.0 81.2 325 44 27.1 8.2 89.4 PAN #N/A 34.9 10.6 100.0 FEEDMATERIAL PROPERTIES DATA SHEET - BATCH 4. CHEMICAL NAME BENTONITEMOLECULAR FORMULA SAMPLE MARKED - LAST SHIPMENT MOISTURE CONTENT % 20.2TRUE DENSITY g/cm³ BULK DENSITY (LOOSE) g/cm³  1.03 BULK DENSITY(PACKED) g/cm³  1.16 HARDINESS MOHS SCALE ANGLE OF REPOSE deg NOTMEASURED ANGLE OF FALL deg ANGLE OF DIFFERENCE deg OTHER MATERIALRETAINED ON SIEVE MASS MASS MESH MICRONS MASS g FRACTION % ACCUMUL %  82380 35.2 9.1 9.1  18 1000 48.5 12.5 21.7  35 500 82.3 21.3 42.9  70 210159.1 41.2 84.1 140 105 33.9 8.8 92.9 200 74 24.5 6.3 99.2 325 44 0.90.2 99.5 PAN #N/A 2.1 0.5 100.0

[0239] TABLE NO. 2 Roll Press Set Up, Test Conditions and ProcessCharacteristics RUN NO. RUN NO. RUN NO. RUN NO. RUN NO. RUN NO. RUN NO.RUN NO. 1 2 3 4 5 6 7 8 TESTED MATERIAL BATCH 1 BATCH 1 BATCH 1 BATCH 1BATCH 1 BATCH 2 BATCH 2 BATCH 2 FEED MATERIAL BULK DENSITY g/cm³ 1.111.11 1.11 1.11 1.11 1.09 1.09 1.09 MACHINE MODEL B-220QC B-220QC B-220QCB-220QC B-220QC B-220QC B-220QC B-220QC ROLLS PART NO. B2487 B2487 B2487B2487 B2487 B2487 B2487 B2487 ROLL DIAMETER mm 305 305 305 305 305 305305 305 NO. OF POCKETS (CORRUGATIONS) 24 24 24 24 24 24 24 24 NO. OFROWS 1 1 1 1 1 1 1 1 ROLL FACE WIDTH mm 76 76 76 76 76 76 76 76 ROLLSPEED rev/min 3.0 3.0 3.0 3.0 14.7 12.4 3.0 3.0 ROLL TORQUE Nm 3672 38152736 2689 2915 3029 3910 ROLL DRIVE POWER INDEX kW 1.16 1.20 0.96 0.864.15 3.80 0.95 1.23 FEED SCREW PART NO. FEED SCREW OUTSIDE DIA mm 73 6363 63 63 63 63 63 FEED SCREW ROOT DIA mm 41 35 35 35 35 35 35 35 FEEDSCREW PITCH mm 51 51 51 51 51 51 51 51 SCREW BARREL INSIDE DIA mm 76 7676 76 76 76 76 76 FEEDSCREWSPEED rev/min 31 58 52 49 391 391 82 91 SCREWTORQUE Nm 284 158 123 115 78.5 45 43 53 FEED SCREW DRIVE POWER IND kW0.92 0.96 0.67 0.59 3.22 1.85 0.37 0.51 PRESSURE IN HYDRAULIC SYS MPaINITIAL ACCUMULATOR PRESSURE MPa 6.89 6.89 6.89 6.89 6.89 6.89 6.89 6.89ROLL SEPARATING FORCE MN 0.184 0.187 0.122 0.069 0.057 0.096 0.105 0.141INITIAL ROLL GAP mm 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 WEB THICKNESS mm 0.70.9 1.2 2.3 2.9 3.1 2.6 2.1 BRIQUET CALCULATED PRESSURE MPa 60.64 61.6340.21 22.74 18.79 31.64 34.60 46.47 RATIO OF TANGENTIAL TO RADIAL STRESS0.13 0.13 0.16 0.26 0.31 0.20 0.19 0.18 MEASURED THROUGHPUT t/h 0.26420.2609 0.2731 0.2945 1.5382 1.3472 0.3127 0.3207 BRIQUET TEMPERATUREDEG.C NOT NOT NOT NOT NOT NOT NOT NOT MEAS MEAS MEAS MEAS MEAS MEAS MEASMEAS BRIQUET WEIGHT g 57.91 57.61 59.48 63.51 66.25 67.52 66.45 69.65BRIQUET NET PRODUCTION RATE t/h 0.2502 0.2489 0.2570 0.2744 1.40241.2056 0.2871 0.3009 FINES PERCENTAGE % 5.3 4.6 5.9 6.8 8.8 10.5 8.2 6.2FEED SCREW EFFICIENCY % 87.6 61.5 71.7 82.1 53.7 47.2 53.1 49.0 ROLLDRIVE ENERGY CONS. kWh/t 4.4 4.6 3.5 2.9 2.7 2.8 3.1 3.8 SCREW DRIVEENERGY CONS. kWh/t 3.5 3.7 2.5 2.0 2.1 1.4 1.2 1.6 RUN NO. RUN NO. RUNNO. RUN NO. RUN NO. RUN NO. RUN NO. RUN NO. 9 10 11 12 13 14 15 16TESTED MATERIAL BATCH 2 BATCH 3 BATCH 3 BATCH 3 BATCH 3 BATCH 4 BATCH 4BATCH 4 FEED MATERIAL BULK DENSITY g/cm³ 1.09 1.16 1.16 1.16 1.16 1.031.03 1.03 MACHINE MODEL B-220QC B-220QC B-220QC B-220QC B-220QC B-220QCB-220QC B-220QC ROLLS PART NO. B2487 B2487 B2487 B2487 B2487 B2487 B2487B2487 ROLL DIAMETER mm 305 305 305 305 305 305 305 305 NO. OF POCKETS(CORRUGATIONS) 24 24 24 24 24 24 24 24 NO. OF ROWS 1 1 1 1 1 1 1 1 ROLLFACE WIDTH mm 76 76 76 76 76 76 76 76 ROLL SPEED rev/min 3.0 3.0 3.0 3.016.4 3.0 3.0 3.0 ROLL TORQUE Nm 5036 5108 3997 2982 4095 2895 2490 2162ROLL DRIVE POWER INDEX kW 1.59 1.61 1.26 0.94 7.05 0.91 0.78 0.68 FEEDSCREW PART NO. FEED SCREW OUTSIDE DIA mm 63 63 73 63 63 63 63 63 FEEDSCREW ROOT DIA mm 35 35 41 35 35 35 35 35 FEED SCREW PITCH mm 51 51 5151 51 51 51 51 SCREW BARREL INSIDE DIA mm 76 76 76 76 76 76 76 76FEEDSCREWSPEED rev/min 94 71 69 82 391 67 66 66 SCREW TORQUE Nm 72 12993 43 67 228 148 76 FEED SCREW DRIVE POWER IND kW 0.71 0.96 0.67 0.372.75 1.60 1.03 0.53 PRESSURE IN HYDRAULIC SYS MPa INITIAL ACCUMULATORPRESSURE MPa 6.89 6.89 6.89 6.89 6.89 6.89 6.89 6.89 ROLL SEPARATINGFORCE MN 0.202 0.205 0.148 0.086 0.153 0.185 0.141 0.084 INITIAL ROLLGAP mm 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 WEB THICKNESS mm 2.0 2.1 2.2 3.12.4 0.7 0.7 0.8 BRIQUET CALCULATED PRESSURE MPa 66.57 67.56 48.78 28.3450.42 60.97 46.47 27.68 RATIO OF TANGENTIAL TO RADIAL STRESS 0.16 0.160.18 0.23 0.18 0.10 0.12 0.17 MEASURED THROUGHPUT t/h 0.3253 0.32310.3061 0.3247 1.7124 0.2571 0.2592 0.2641 BRIQUET TEMPERATURE DEG.C NOTNOT NOT NOT NOT NOT NOT NOT MEAS MEAS MEAS MEAS MEAS MEAS MEAS MEASBRIQUET WEIGHT g 70.51 69.82 66.85 70.50 66.15 56.85 56.72 57.95 BRIQUETNET PRODUCTION RATE t/h 0.3046 0.3016 0.2888 0.3046 1.5622 0.2456 0.24500.2503 FINES PERCENTAGE % 6.4 6.6 5.7 6.2 8.8 4.5 5.5 5.2 FEED SCREWEFFICIENCY % 48.1 59.5 50.1 51.8 57.2 56.5 57.8 58.9 ROLL DRIVE ENERGYCONS. kWh/t 4.9 5.0 4.1 2.9 4.1 3.5 3.0 2.6 SCREW DRIVE ENERGY CONS.kWh/t 2.2 3.0 2.2 1.1 1.6 6.2 4.0 2.0 RUN NO. RUN NO. RUN NO. RUN NO. 1718 19 20 TESTED MATERIAL BATCH 4 BATCH 4 BATCH 1 BATCH 2 FEED MATERIALBULK DENSITY g/cm³ 1.03 1.03 1.11 1.09 MACHINE MODEL B-220QC B-100RB-400A B-400A ROLLS PART NO. B2487 B1116-4 B4609 B4609 ROLL DIAMETER mm305 130 460 460 NO. OF POCKETS (CORRUGATIONS) 24 18 22 22 NO. OF ROWS 12 2 2 ROLL FACE WIDTH mm 76 51 152 152 ROLL SPEED rev/min 15.1 3.0 2.42.4 ROLL TORQUE Nm 2308 520 10800 18500 ROLL DRIVE POWER INDEX kW 3.660.16 2.72 4.66 FEED SCREW PART NO. B469 B469 FEED SCREW OUTSIDE DIA mm63 44 140 140 FEED SCREW ROOT DIA mm 35 19 95 95 FEED SCREW PITCH mm 5140 76 76 SCREW BARREL INSIDE DIA mm 76 51 148 148 FEEDSCREWSPEED rev/min391 57 48 73 SCREW TORQUE Nm 65 79 420 285 FEED SCREW DRIVE POWER IND kW2.67 0.47 2.12 2.49 PRESSURE IN HYDRAULIC SYS MPa INITIAL ACCUMULATORPRESSURE MPa 6.89 6.89 6.89 6.89 ROLL SEPARATING FORCE MN 0.086 0.0540.210 0.399 INITIAL ROLL GAP mm 0.4 0.6 1.0 1.0 WEB THICKNESS mm 0.9 0.71.2 3.3 BRIQUET CALCULATED PRESSURE MPa 28.34 46.67 21.03 39.96 RATIO OFTANGENTIAL TO RADIAL STRESS 0.18 0.15 0.22 0.20 MEASURED THROUGHPUT t/h1.3247 0.0432 1.0215 1.1805 BRIQUET TEMPERATURE DEG.C NOT NOT NOT NOTMEAS MEAS MEAS MEAS BRIQUET WEIGHT g 57.45 6.15 161.22 186.31 BRIQUETNET PRODUCTION RATE t/h 1.2492 0.0399 1.0215 1.1805 FINES PERCENTAGE %5.7 7.7 NOT NOT MEAS MEAS FEED SCREW EFFICIENCY % 49.9 24.8 50.6 39.2ROLL DRIVE ENERGY CONS. kWh/t 2.8 3.8 2.7 3.9 SCREW DRIVE ENERGY CONS.kWh/t 2.0 10.9 2.1 1.8

[0240] TABLE 3 Product Evaluation RUN NO. 1 RUN NO. 2 RUN NO. 3 RUN NO.4 RUN NO. 5 RUN NO. 6 BRIQUETWEIGHT g 57.54 57.43 58.46 65.45 66.5268.72 BRIQUETVOLUME cm3 27.27 27.22 27.84 31.32 31.98 32.72BRIQUETDENSITY g/cm3 2.11 2.11 2.10 2.09 2.08 2.10 BRIQUETS BULK DENSITYt/m3 NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS.BRIQUETS “GREEN” STRENGTH MEAN CRUSHING FORCE N 1325.5 1227.6 1245.41316.6 1076.4 1797.1 DROP HEIGHT AT FAILURE m 2.0 2.0 2.0 2.0 2.0 1.8NUMBER OF DROPS 6 6 17 8 10 1 RUN NO. 7 RUN NO. 8 RUN NO. 9 RUN NO. 10RUN NO. 11 RUN NO. 12 BRIQUETWEIGHT g 65.01 70.37 70.52 70.29 66.5970.28 BRIQUETVOLUME cm3 30.81 32.28 32.05 32.09 30.83 33.31BRIQUETDENSITY g/cm3 2.11 2.18 2.20 2.19 2.16 2.11 BRIQUETS BULK DENSITYt/m3 NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS.BRIQUETS “GREEN” STRENGTH MEAN CRUSHING FORCE N 1556.8 1859.3 2143.92215.1 >2224 1663.5 DROP HEIGHT AT FAILURE m 1.5 1.2 2.0 1.8 2.0 1.2NUMBER OF DROPS 1 1 2 1 2 1 RUN NO. 13 RUN NO. 14 RUN NO. 15 RUN NO. 16RUN NO. 17 RUN NO. 18 BRIQUETWEIGHT g 66.02 55.48 56.79 57.61 57.66 6.14BRIQUETVOLUME cm3 30.85 25.93 26.41 26.92 26.94 2.84 BRIQUETDENSITYg/cm3 2.14 2.14 2.15 2.14 2.14 2.16 BRIQUETS BULK DENSITY t/m3 NOT MEAS.NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS. NOT MEAS. BRIQUETS “GREEN”STRENGTH MEAN CRUSHING FORCE N 2046.1 1192.0 1227.6 1120.9 1014.2 427.1DROP HEIGHT AT FAILURE m 1.2 2.0 2.0 2.0 2.0 2.0 NUMBER OF DROPS1 >20 >20 >20 >20 >20 RUN NO. 19 RUN NO. 20 BRIQUETWEIGHT g 161.22186.31 BRIQUETVOLUME cm3 NOT MEAS. NOT MEAS. BRIQUETDENSITY g/cm3 NOTMEAS. NOT MEAS. BRIQUETS BULK DENSITY t/m3 NOT MEAS. NOT MEAS. BRIQUETS“GREEN” STRENGTH MEAN CRUSHING FORCE N 1147.6 1912.6 DROP HEIGHT ATFAILURE m 2.0 1.5 NUMBER OF DROPS 6 1

[0241] TABLE 4 ROLL HYDRAULIC CYCLES/ SCREW PRESSURE LOAD CYLCES/ (psi)(Hz/A) LOAD Hz/A) RESULTS MATERIAL: BENTONITE @0% MOISTURE RUN 1 70060/21.19 10/20.07 Briquets appear crushed and brittle. RUN 2 70060/23.16 13/17.35 No great improvement in briquet quality. RUN 3 60058/23.05 11/20.13 Slightly stronger briquets, pressure sensitive. RUN 4700 58/23.35 11/19.89 Quality improved, but pressure sensitive. RUN 5850 58/? 13/? Best looking briquets. RUN 6 600 58/36.71 13/20.92 Goodbriquets, but with cracks. RUN 7 500 58/33 11/? Best briquets but highpressure fluctuations. RUN 8 500 60/22.33 11/19.67 Moderate briquets.RUN 9 400 58/23 11/19.9 About the same as RUN 8. MATERIAL: BENTONITE @7%MOISTURE RUN 1 400 56/24 11/19.6 Good briquets, but not well-filled.Surface had cracks. RUN 2 300 56/24.9 11/21.5 Briquets same as RUN 1,but had fewer surface cracks. RUN 3 300 56/21.8 10/20.7 Briquets wereweaker and not well-filled. More lines generated. RUN 4 300 54/27.011/20.1 Quality improved, briquet was much fuller and strong. RUN 5 30052/20.4 17.1 Best looking briquets. Green strength very high, a bit moreflashing, but break off easily in tumbler. NOTE: Hydraulic pressurefluctuates 300-600 psi indicated depending on material flow from bucketelevator. MATERIAL: BENTONITE @14% MOISTURE RUN 6 300 52/21.86 11/19.03Thicker, stickier material results in better quality briquet:well-filled and high in green strength. There are surface cracks. RUN 7300 58/21.5 11/20.6 Briquets are crumbly and wea, very few arewell-formed. Rough edges on most briquets. RUN 8 300 58/24.4 13/19.3Better briquet than previous runs, some surface cracks, but less thanbefore. RUN 9 300 58/25.1 13/20.3 Run withbelt slippage in mind. Longerrun produced briquets like RUN 8 but a bit more splitting and/or minimalclamshelling. RUN 10 300 58/? 15/? Run to see max feed screw speed.Belts slipped, motor tripped. RUN 11 200 58/? 14/? Same objective andresults as RUN 10, with less pressure to reduce load. RUN 12 200 54/?13/? Same results as RUN 11, this run was made with roll and screw speeddecreased for reduced loading (pressure also reduced). RUN 13 20045/20.9 6/20.0 Objective was to determine minimum speeds and pressures.Fines were generated, not briquets. RUN 14 200 58/29.6 13/20.11 Briquetswere full, but feeder motor trips after short run. RUN 15 400 58/31.313/18.7 Belts slipped immediately, feed motor tripped. RUN 16 30058/24.1 12/21.4 Good briquets, but with some surface cracks and flash.Green strength was high. RUN 17 250 58/30.3 58/21.0 Very good briquetwith some flash, no cracks. Full briquet with high green strength. RUN18 250 60/? 15/? Immediate belt slippage and trip RUN 19 250 58/2311/20.0 Most full briquet of all previous runs, but edges not clean. Nocracks, no splitting, high strength. RUN 20 250 56/22.3 11/21.6 Aboutthe same as RUN 19, but run at a slower capacity. RUN 21 300 58/26.313/19.3 Briquets are satisfactory, but highly sensitive to hydraulicpressure. Higher tendency to show splitting. RUN 22 250 58/22.1 12/21.4Best briquet of all previous trials, but still slightly sensitive tohydraulic pressure, though not problematic. No cracks on surface,consistent quality, high strength. RUN 23 250 60/22.4 13/19 Best briquetfor highest capacity. No cracks or splitting. Consistently good qualityand high strength.

[0242] TABLE 3 COALINGA PILOT ABANDONMENT RESULTS Top Well Top InitialBot. “A” Pt Well Type Case TD Perf Fluid L. Plug Fluid L 60-11A Producer1 2,680 2,360 1,297 2,240 NA 2-8-11A Producer 1 1,660 1,449 — 1,196 NA3-7-11A Producer 1 1,880 1,166 482 1,465 NA 146-11A Producer 1 1,8001,604 1,400 1,462 NA 45-11A Producer 1 1,600 1,503 1,460 1,407 NA243-11A Producer 1 1,800 1,617 1,455 1,487 NA 138-11A Producer 1 1,6221,432 1,270 1,281 NA Amity 9- Cyclic 1 973 447 355 342 NA 3-1D 8-4A-1DCyclic 1 605 162 50 1 NA 2-8-25D Cyclic 1 1,130 885 720 529 NA 2-7-25DCyclic 1 1,150 1,006 720 810 NA 2-9-7C Cyclic 2 1,820 1,500 1,320 1,3721,091 1-7-19C Cyclic 2 1,900 1,642 — 1,554 1,303 4-8-7C Producer 2 1,8001,673 700 1,573 1,237 4-7-7C Producer 2 1,810 1,681 280 1,558 1,1474-7-17C Water Inj 3 3,405 3,278 380 3,141 2,322 3-6-17C Water Inj 33,270 3,152 350 2,985 2,316 Arica 6- Producer 3 2,095 1,984 — 1,8501,468 6-7C Arica 5- Producer 3 1,965 1,842 480 1,763 1,382 6-7C TopFresh T/Fresh Surf. Top Aban. Doggr “A” Pt Water Water Fluid Surf. TimeAp- Well Plug Fluid L. Plug L. Plug (hrs) proval 60-11A NA NA NA 480 1012.5 Yes 2-8-11A NA NA NA 504 9 15.5 Yes 3-7-11A NA NA NA — 10 7 Yes146-11A NA NA NA — 8 11 Yes 45-11A NA NA NA 355 11 6.5 Yes 243-11A NA NANA at 3 6 Yes surf 138-11A NA NA NA — 8 4.5 Yes Amity 9- NA NA NA at 114.5 Yes 3-1D surf 8-4A-1D NA NA NA at NA 4 Yes surf 2-8-25D NA NA NA at9 7 Yes surf 2-7-25D NA NA NA at 1 5 Yes surf 2-9-7C 1,091 at surf 232at 9 6.5 Yes surf 1-7-19C 1,303 at surf 352 at 11 7 Yes surf 4-8-7C1,237 at surf 399 at 10 7 Yes surf 4-7-7C 1,147 at surf 355 — 10 19.5Yes 4-7-17C 2,322  98 1,041 — 1 27.5 Yes 3-6-17C 2,316 at surf 1,117 at13 7.5 Yes surf Arica 6- 1,468 106 507 at 8 10 Yes 6-7C surf Arica 5-1,382 at surf 567 — 8 28 Yes 6-7C

What is claimed is:
 1. A material for plugging a well comprisingcompacted nodules comprising bentonite in admixture with a proportion ofwater to permit the formation of compacted nodules having a density ofat least about 2.0 g/cm³ and a mean particle survival at a crush forceof at least 800 newtons and being capable of having at least 50%survival when dropped 1.5 meters onto a concrete surface.
 2. A materialfor plugging a well of claim 1 comprising from about 35% to about 98% byweight bentonite, from about 0% to about 45% by weight nonbentonitesolids, and from about 2% to about 20% by weight nonconnate water, saidmaterial being in the form of compacted nodules.
 3. A material forplugging a well of claim 1 comprising from about 45% to about 95% byweight bentonite, from about 0% to about 35% by weight nonbentonitesolids, and from about 5% to about 20% by weight nonconnate water. 4.The material for plugging a well of claim 1 comprising from about 50% toabout 90% by weight bentonite, from about 0% to about 30% by weightnonbentonite solids, and from about 10% to about 20% by weightnonconnate water.
 5. The material for plugging a well of claim 2comprising from about 64% to about 88% by weight bentonite, from about0% to about 20% by weight nonbentonite solids, and from about 12% toabout 16% by weight nonconnate water.
 6. The material for plugging adrill hole of claim 1 consisting essentially of from about 85% to about90% by weight sodium bentonite and from about 10% to about 15% by weightnonconnate water.
 7. The material for plugging a well of claim 1 whereinsaid compacted nodules are substantially pillow shaped with a largestcross sectional dimension is from about ⅞ inch to about 4 inches.
 8. Thematerial for plugging a well of claim 1 wherein said largest crosssectional dimension of from about 1 inch to about 4 inches.
 9. Thematerial for plugging a well of claim 1 wherein said compacted nodulesare in the form of spheres having a diameter of from about 1 inch toabout 4 inches.
 10. The material for plugging a well of claim 1 whereinsaid compacted nodules are in the form of flattened spheres having amajor diameter of from about 1 inch to about 4 inches and a minordiameter wherein the minor diameter is from about 0.50 to 0.99 times themajor diameter.
 11. A method for forming a material for plugging a wellcomprising a. obtaining a feedstock comprising bentonite in admixturewith a proportion of water to permit the formation of compacted noduleshaving a density of at least 2.0 g/cm³ and a mean particle survival at acrush force of at least 800 newtons and capable of having at least 50%survival when dropped 1.5 meters onto a concrete surface, b. feeding thefeedstock under pressure to a continuous roll press machine underconditions to permit the formation of said compacted nodules and c.recovering the compacted nodules.
 12. The method of claim 11 wherein thefeedstock comprises from about 35% to about 98% by weight bentonite,from about 0% to about 45% by weight nonbentonite solids, and from about2% to about 20% by weight nonconnate water.
 13. The method of claim 11wherein the feedstock comprises from about 45% to about 95% by weightbentonite, from about 0% to about 35% by weight nonbentonite solids, andfrom about 5% to about 20% by weight nonconnate water.
 14. The method ofclaim 11 wherein the feedstock comprises from about 64% to about 88% byweight bentonite, from about 0% to about 20% by weight nonbentonitesolids, and from about 12% to about 16% by weight nonconnate water. 15.The method of claim 11 wherein the feedstock consists essentially offrom about 85% to about 90% by weight bentonite and from about 10% toabout 15% by weight nonconnate water.
 16. The method of claim 11 whereinthe pressure is a pressure of at least about 1 Mpa.
 17. The method ofclaim 11 wherein the pressure is a pressure of at least about 3 Mpa. 18.The method of claim 11 wherein the pressure is a pressure of at leastabout 5 Mpa.
 19. The method of claim 11 wherein said continuousmanufacturing machine is a roller press.
 20. The method of claim 11wherein said roller press is operated at a speed of from about 2 RPM toabout 50 RPM.
 21. A material for plugging a well, said material being inthe form of compacted nodules having a density of at least 2.0 g/cm³,and a mean particle survival at a crush force of at least 800 newtonsand capable of having at least 50% survival when dropped 1.5 meters ontoa concrete surface, said material being formed by the process comprisinga. obtaining a feedstock comprising sodium bentonite in admixture with aproportion of water to permit the formation of compacted nodules havinga density of at least 2.0 g/cm³, and a mean particle survival at a crushforce of at least 800 newtons and capable of having at least 50%survival when dropped 1.5 meters onto a concrete surface. b. feeding thefeedstock under pressure to a continuous roll press machine underconditions to permit the formation of said compacted nodules and c.recovering the compacted nodules.
 22. A method for plugging a wellhaving a bottom, a length and an opening at a surface comprising: a.introducing a plurality of nodules into the well, said nodulescomprising bentonite in admixture with a proportion of water to permitthe formation of compacted nodules having a density of at least 2.0g/cm³, and a mean particle survival at a crush force of at least 800newtons and capable of having at least 50% survival when dropped 1.5meters onto a concrete surface, b. permitting the introduced nodules tocome in contact with additional water, in an amount and for a timeadequate to cause the nodules to swell and form a substantiallyhydraulically solid plug in the well.
 23. The method of claim 22 whereinsaid nodules are introduced into the bottom of the well by falling fromsaid opening to said bottom.
 24. The method of claim 22 wherein saidnodules are introduced over the length of the well.
 25. The method ofclaim 22 wherein said nodules are introduced over at least one portionof the length of the well and wherein nonbentonite material isintroduced into at least one other portion of the length of the well.26. The method of claim 22 wherein heat is introduced into the well. 27.The method of claim 22 wherein the well contains viscous material andwherein hot water is introduced into the well to reduce the viscosity ofsaid viscous material.
 28. The method of claim 22 wherein the hot wateris introduced into the well prior to introducing the nodules.
 29. Themethod of claim 22 wherein the well contains saline water.
 30. Themethod of claim 22 wherein the nodules contain additional water tocompensate for the salinity in the saline water.
 31. The method of claim22 wherein the compacted nodules are substantially pillow shaped with alargest cross sectional dimension of from about 1 inch to about 6inches.
 32. The method of claim 22 wherein the compacted nodules are inthe form of spheres having a diameter of from about 1 inch to about 6inches.
 33. The method of claim 22 where the compacted nodules are inthe form of flattened spheres having a major diameter of from about 1inch to about 6 inches and a minor diameter which is from about 0.99 to0.50 times the major diameter.